Polo Scienze per Immagini, di Laboratorio e Infettivologiche, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli, Largo Francesco Vito, 1-00168, Rome, Italy.
Institut fuer Klinische Genetik, Medizinische Fakultaet Carl Gustav Carus, Technische Universitaet Dresden, Fetscherstr. 74, 01307, Dresden, Germany.
Mol Diagn Ther. 2017 Oct;21(5):539-545. doi: 10.1007/s40291-017-0288-6.
Many studies document the involvement of BRCA1/2 gene rearrangements in genetic predisposition to breast and ovarian cancer. Large genomic rearrangements (LGRs) of BRCA1 account for 0-27% of all disease-causing mutations in various populations, while LGRs in BRCA2 are rarer. Here, we describe a novel BRCA2 LGR, involving the duplication of exons 4-26, in an Italian family with hereditary breast and ovarian cancer (HBOC) syndrome.
Our purpose was to provide an effective characterization of this variant using a combination of different methods able to establish the exact breakpoints of the duplication.
A multiplex amplicon quantification (MAQ) assay was used as the primary screening method in the detection of LGRs. Array comparative genomic hybridization (CGH), reverse transcriptase polymerase chain reaction (RT-PCR) and long-range PCR were used for the careful characterization of the rearrangement and breakpoint regions. The Repeat Masker program was employed to identify Alu sequences at breakpoint junctions.
Array CGH and long-range PCR strategies revealed that the BRCA2 exons 4-26 duplication (g.12016_87170dup) involved exactly 75,154 bp nucleotides between intron 3 and intron 26 of the gene. Given that no Alu repeats were found at the junction sites, we support the hypothesis that the new duplication could be the result of a microhomology-mediated event (MH) involving very short homologous sequences at an upstream breakpoint.
LGR investigation is mandatory in BRCA1/2 routine testing in order to provide a complete result for a targeted therapeutic decision. Nevertheless, the characterization and classification of novel BRCA1/2 variants represents a crucial step in the support of genetic counselling. Our results, including a comprehensive co-segregation analysis, indicate that the novel duplication identifed has a pathogenic role and would be considered a causing-disease variant in genetic and oncologic counselling.
许多研究证明 BRCA1/2 基因重排与乳腺癌和卵巢癌的遗传易感性有关。BRCA1 的大片段重排（LGR）占各种人群中所有致病突变的 0-27%，而 BRCA2 中的 LGR 则较为罕见。在这里，我们描述了一个意大利遗传性乳腺癌和卵巢癌（HBOC）综合征家族中涉及外显子 4-26 重复的新型 BRCA2 LGR。
我们的目的是使用能够确定重复的精确断点的不同方法的组合，对该变体进行有效的特征描述。
多重扩增子定量（MAQ）检测作为检测 LGR 的主要筛选方法。使用阵列比较基因组杂交（CGH）、逆转录聚合酶链反应（RT-PCR）和长距离 PCR 对重排和断点区域进行仔细特征描述。使用重复掩蔽程序识别断点连接处的 Alu 序列。
阵列 CGH 和长距离 PCR 策略表明，BRCA2 外显子 4-26 重复（g.12016_87170dup）涉及基因内 3 号内含子和 26 号内含子之间的精确 75154bp 核苷酸。由于在连接位点未发现 Alu 重复序列，我们支持这样的假设，即新的重复可能是微同源介导事件（MH）的结果，该事件涉及上游断点处非常短的同源序列。
为了提供针对靶向治疗决策的完整结果，在 BRCA1/2 常规检测中必须进行 LGR 研究。然而，新型 BRCA1/2 变体的特征描述和分类是遗传咨询支持的关键步骤。我们的结果包括全面的共分离分析，表明鉴定出的新型重复具有致病性作用，并且在遗传和肿瘤咨询中可被视为致病变异。
